1. Field
The present invention relates to a dimmable alternating current (AC) driven light emitting diode (LED) illuminating apparatus, and more particularly, to an AC driven light emitting diode (LED) illuminating apparatus capable of displaying an appropriate dimming level over an entire section of the dimming level using a TRIAC dimmer configured to perform dimming control via phase control.
2. Discussion of the Background
Generally, a diode device for light emission such as a light emitting diode (LED) has been driven only by direct current (DC) power due to diode characteristics. Therefore, a light emitting apparatus using an LED according to the related art has been restrictively used, and should include a separate circuit such as a switching mode power supply (SMPS) in order to be driven by alternating current (AC) power of 220V that is currently used at home. Therefore, a circuit of the light emitting apparatus has become complicated, and a cost required for manufacturing the light emitting apparatus has increased.
In order to solve these problems, research into an LED that may be driven even by AC power by connecting a plurality of light emitting cells in series with or parallel with each other has been actively conducted.
In order to solve the problems in the related art as described above, a sequential driving scheme of LEDs using AC power has been suggested. According to the sequential driving scheme, when an illuminating apparatus including three LED groups is assumed, in a situation in which an input voltage is increased over time, a first LED group first starts to emit light at Vf1, a second LED group connected in series with the first LED group starts to emit light at Vf2 higher than Vf1, and a third LED group connected in series with the second LED group and the first LED group starts to emit light at Vf3 higher than Vf2. In addition, in a situation in which the input voltage is decreased over time, the third LED group stops emitting the light at Vf3, the second LED group stops emitting the light at Vf2, and the first LED group finally stops emitting the light at Vf1, such that an LED driving current is designed so as to be approximate to the input voltage.
Meanwhile, a dimming control of the LED indicates that a luminescent flux or an illumination (Lux) of an LED illuminating apparatus, that is, generally, a brightness of a light source is changed depending on an applied supplying voltage, and a dimmable light source means an apparatus performing the above-mentioned illumination control function in the illuminating apparatus. This LED dimmable system is included in the LED illuminating apparatus in order to decrease power consumption of the LED illuminating apparatus and efficiently operate the LED illuminating apparatus. Particularly, heat generated due to a continuous light emitting operation of the LED is a factor of decreasing quality and efficiency of an illuminating operation. Therefore, in order to reflect a demand by a user and decrease power consumption, a dimming function has been generally added to the LED illuminating apparatus. Among the LED illuminating apparatuses to which the dimming function is added, the LED illuminating apparatus using the DC power as described above is driven by converting the AC power into the DC power using the SMPS. Therefore, dimming is relatively easy, such that dimming control characteristics may be expected to some degree.
However, in the case of the AC driven LED illuminating apparatus as described above, the LED is driven only by a voltage generated by rectifying the AC power, such that it is not easy to implement a dimming function and it is difficult to secure linearity in a dimming control. Particularly, in the case of an AC driven LED illuminating apparatus using the sequential driving scheme, since a driving voltage fluctuates due to a phenomenon that a power supply voltage temporally descends or ascends simultaneously with turning on/off the LEDs at the next step due to internal impedances of an AC power supplying line and a dimmer at a point in time in which the number of LED groups light-emitted depending on a magnitude of the driving voltage is changed (for example, a change point in time from 1-stage driving to 2-stage driving, a change point in time from 2-stage driving to 3-stage driving, or the like), that is, a change point in time in which the driving voltage divided into two stages or more is exceeded, such that an unstable phenomenon may occur. That is, in the case of the AC driven LED illuminating apparatus having the dimming function according to the related art, ideal illumination change characteristics do not appear over an entire section of a dimming level, and a phenomenon that a luminescent flux is irregularly changed in a portion of a dimming control section occurs.